NSDate和NSString的转换及判定是昨天，今天，明天

用于uidate，picker。。

+(NSDate*) convertDateFromString:(NSString*)uiDate
{
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;
    [formatter setDateFormat:@"yyyy年MM月dd日"];
    NSDate *date=[formatter dateFromString:uiDate];
    return date;
}

-(NSString *)getCurrentTime:(NSDate *)date{

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];

[formatter setDateFormat:@"yyyy-MM-dd HH:MM:SS"];

NSString *dataTime = [formatter stringFromDate:date];

return dataTime;

}

//判定是昨天，今天，明天

-(NSString *)compareDate:(NSDate *)date{

NSTimeInterval secondsPerDay = 24 * 60 * 60;

NSDate *today = [[NSDate alloc] init];

NSDate *tomorrow, *yesterday;

tomorrow = [today dateByAddingTimeInterval: secondsPerDay];

yesterday = [today dateByAddingTimeInterval: -secondsPerDay];

// 10 first characters of description is the calendar date:

NSString * todayString = [[today description] substringToIndex:10];

NSString * yesterdayString = [[yesterday description] substringToIndex:10];

NSString * tomorrowString = [[tomorrow description] substringToIndex:10];

NSString * dateString = [[date description] substringToIndex:10];

if ([dateString isEqualToString:todayString])

{

return @"今天";

} else if ([dateString isEqualToString:yesterdayString])

{

return @"昨天";

}else if ([dateString isEqualToString:tomorrowString])

{

return @"明天";

}

else

{

return dateString;

}

}

输入的日期字符串形如：@"1992-05-21 13:08:08"

- (NSDate *)dateFromString:(NSString *)dateString{

NSDateFormatter *dateFormatter = [[NSDateFormatteralloc] init];

[dateFormatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];

NSDate *destDate= [dateFormatter dateFromString:dateString];

[dateFormatter release];

return destDate;

}

- (NSString *)stringFromDate:(NSDate *)date{

NSDateFormatter *dateFormatter = [[NSDateFormatteralloc] init];

//zzz表示时区，zzz可以删除，这样返回的日期字符将不包含时区信息。

[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss zzz"];

NSString *destDateString = [dateFormatter stringFromDate:date];

[dateFormatter release];

return destDateString;

}

- (IBAction)handleDidPressBtn1{

NSLog(@"%@/n", [selfdateFromString:@"2011-08-09 12:02:01"]);

NSLog(@"%@/n", [selfstringFromDate:[selfdateFromString:@"2011-08-09 12:02:01"]]);

}

输出结果如下：

2011-08-09 04:02:01 +0000

2011-08-09 12:02:01 GMT+08:00